Mar. 19, 2013

Last July, NASA's High Resolution Coronal Imager captured the highest-resolution images ever taken of the sun's corona. / NASA

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This Extreme Ultraviolet Imaging Telescope image of a huge, handle-shaped prominence was taken on Sept. 14,1999. Prominences are huge clouds of relatively cool dense plasma suspended in the Sun's hot, thin corona. At times, they can erupt, escaping the Sun's atmosphere. / NASA/European Space Agency

Shedding more light on the subject

ē The sunís mass is 333 million times that of Earthís. ē On average, the sun is about 93 million miles from Earth. Its light takes eight minutes to get here. ē In addition to light, the sun sends out solar wind, which is a stream of charged particles moving away from the sun at about 250 miles per second. Earth is protected from much of these by the planetís magnetic field. ē Sunspots are cooler regions on the sunís photosphere. A sunspot can last from a few hours to a few months. ē Each second, the sun transforms 700 million tons of hydrogen gas into 695 million tons of helium gas. The remaining 5 million tons of matter escape as energy. Source: nasa.com and cde.nwc.edu

With an equatorial circumference of 2.7 million miles, about 1 million Earths could fit inside the sun. The temperature of its surface is about 10,000 degrees Fahrenheit. / Getty Images

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The sun is our source of light and heat. We see its light every day, even when itís cloudy, and without its heat, Earth would be too cold to support any life. But what is it, exactly?

The sun is a star. Like other stars, it is essentially an extremely large nuclear power plant.

With an equatorial circumference of 2.7 million miles, about 1 million Earths could fit inside it. At its core, the sun is a cozy 27 million degrees Fahrenheit. That temperature allows the sun to maintain thermonuclear fusion.

The sunís core, with its extreme heat and gravitational pressure, converts hydrogen into helium.

The process takes more than one step and is complex, but the result is that when hydrogen atoms fuse to create helium atoms, some energy is released.

That energy is carried toward the sunís surface by radiation. It takes about 170,000 years for the energy to get from the core to the sunís convective zone, where the temperature drops to 3.5 million degrees.

The sunís surface, which is also called the photosphere, is a 300-mile-thick region where radiation escapes outward and is seen on Earth as sunlight. The temperature of the photosphere is about 10,000 degrees.

Surrounding the sun is its corona, where plasma streams away from the sun. Normally, the corona is not visible, but it can be seen during a total solar eclipse, when the moon blocks out the much brighter photosphere.

Interestingly, the corona is much hotter than the surface, reaching temperatures as high as 3.5 million degrees.

The sun's end

The sunís gravity and thermonuclear fusion balance each other. Without the gravity, the fusion would rip it apart. And without the outward pressure of fusion, the sunís intense gravity would cause it to collapse.

The sun has been producing energy for about 4.5 billion years and has enough hydrogen to produce energy about that much longer.

When it is no longer able to maintain fusion, the sunís gravity will win out and cause the star to collapse. When it collapses, the core will get much denser and heat up. That will cause it to expand many times its original size into a red giant star.

After about 100 million years, most of the star will blow off into space and leave behind an Earth-sized white dwarf that will eventually cool completely.